The Uniting Church in Australia has made an offer to the Australian Government to care for unaccompanied children being held in offshore immigration detention centres.

The government's border protection policy mandates that all asylum seekers, including unaccompanied minors, who arrive in Australia by boat must be sent offshore for processing.

The Uniting Church says it wants to stop children without parents being sent to facilities on Christmas Island and Nauru.

Reverend Elenie Poulos says children sent to the facilities are at risk of serious and permanent harm.

"The Uniting Church has a long history in caring for asylum seekers and we have made an offer to the government to provide sanctuary for all of those child asylum seekers without parents," she said.

"We'd like to see them in our care where they can get the best care possible."

Reverend Poulos says the Church believes there are around 30 unaccompanied minors currently in detention on Christmas Island.

"It's very difficult to get confirmed statistics and numbers from the government," she said.

"It is our understanding that there are around 30 children without parents in detention on Christmas Island, the youngest of whom is 12."

The Australian government is yet to respond to the Church's offer.

Last month the Immigration Minister Scott Morrison stood by the government's policy of placing children in offshore detention in Nauru and the way he carries out his responsibilities as the legal guardian of unaccompanied minors.

"I do that by ensuring that the facilities are in place in Nauru and when my guardianship responsibilities are transferred to the justice minister in Nauru, that's how I do it and that's what I've been doing," he said.